1. Field of the Invention
The invention relates to a process for the desulfurization and demetalation of nickel and sulfur containing heavy hydrocarbon charge stocks.
2. Description of the Prior Art
Heavy hydrocarbon charge stocks, such as residual petroleum oil fractions, that is, those heavy fractions produced by atmospheric and vacuum crude distillation columns, are typically characterized as being undesirable as feed stocks for most refining processes due primarily to their high metal and sulfur content. The presence of high concentrations of metals and sulfur and compounds thereof precludes the effective use of such residua as chargestocks for cracking, hydrocracking and coking operations as well as limiting the extent to which such residua may be used as fuel oil. Perhaps the single most undesirable characteristic of such feedstocks is the high metals content. Principal metal contaminants are nickel and vanadium, with iron and small amounts of copper also sometimes present. Additionally, trace amounts of zinc and sodium are found in some feedstocks. As the great majority of these metals, when present in crude oil, are associated with very large hydrocarbon molecules, the heavier fractions produced by crude distillation contain substantially all the metal present in the crude, such metals being particularly concentrated in the asphaltene residual fraction. The metal contaminants are typically large organometallic complexes such as metal prophyrins and asphaltenes.
Processes for desulfurization of such charge stocks are known, but many of these processes are not suited to effect metal removal. In U.S. Pat. No. 3,720,602, a process for the hydrodesulfurization of substantially non-metal containing hydrocarbon feeds is described. This process involves the use of specific vanadium-containing catalyst and injection of water into the desulfurization reactor to effect cooling and to enhance catalyst activity. Water thus injected is separated from the reactor effluent for recycle. Water injection between the catalyst beds of a multi-bed desulfurization reactor is disclosed in U.S. Pat. No. 3,753,894. In this reference, it was reported that processing petroleum residuum feeds with hydrogen plus 10 volume percent water effects a supression of the normal catalyst deactivation rate particularly during the initial period of the product run.
Other disclosures have been made concerning the use of water in desulfurization. Asphaltene-containing black oil is desulfurized by admixing the oil with between 2.0% to about 30.0%, by weight, of water, then reacting with hydrogen at desulfurization conditions over a desulfurization catalyst in U.S. Pat. No. 3,501,396. In U.S. Pat. No. 3,453,206, it is disclosed that in plural stage hydrorefining of petroleum crude oils and the heavier hydrocarbon fractions obtained therefrom, water may be used in the second or catalytic stage, when it is desired to maximize gasoline boiling range hydrocarbons in the product as distinguished from maximizing middle distillate hydrocarbons. Both U.S. Pat. Nos. 3,471,398 and 3,475,324 are related to improved hydrocarbon quench methods in the desulfurization of high boiling hydrocarbons. These patents disclose that it has been found appropriate to add water to the reaction zone in admixture with the charge stock in some instances, however, the use of water is not normally necessary or desirable.
None of the above references disclose the novel desulfurization and demetalation process of this invention.